334 / 471
(
d
)
Anhydrous sodium sulfate
.—Analytically pure. Baked at 650°C for 4 h and stored in a desiccator.
C. Materials
(
a
)
SPE cartridges
.—Cleanert TPT (2000 mg, 12 mL; Agela, Tianjin, People’s Republic of China) or
EnviCarb/PSA (500 mg/500 mg, 6 mL; Supelco, Bellefonte, PA, USA) or equivalent.
(
b
)
SPE tube adapter
.—For 12 mL SPE tubes (57267), for 6 mL SPE tubes (57020-U; Sigma-Aldrich
Shanghai Trading Co., Ltd, Shanghai, People’s Republic of China) or equivalent.
(
c
)
Disposable flow control valve liners
.--For Visiprep TM-DL (57059; Sigma-Aldrich Shanghai Trading Co.,
Ltd).
(
d
)
Pear-shaped flask
.—80 mL (Z680346-1EA; Sigma-Aldrich Shanghai Trading Co., Ltd), or equivalent.
See
Figure
2014.09A
.
(
e
)
Reservoir
.—30 mL (A82030; Agela), or equivalent.
See
Figure
2014.09A
.
(
f
)
Centrifuge tube
.—80 mL.
(
g
)
Millipore filter membrane (nylon)
.—13 mm × 0.2 μm.
D. Preparation of Standard Solutions
(
a
)
Preparation of stock solutions.--
Accurately weigh 5-10 mg of individual pesticide and chemical
pollutants standards (accurate to 0.1 mg) into a 10 mL volumetric flask. Dissolve and dilute to volume
with methanol, toluene, acetone, acetonitrile, isooctane, etc., depending on each individual compound’s
solubility. All standard stock solutions are stored in the dark at 0-4
°
C and can be used for 1 year.
(
b
)
Preparation of mixed standard solution.--
Depending on properties and retention times of
compounds, all compounds are divided into a series of groups. The concentration of each compound is
determined by its sensitivity on the instrument for analysis. Mixed standard solutions are stored in the
dark below 4°C.
(
c
)
Working standard mixed solution in matrix.--
Working standard mixture solution in matrix of pesticide
and chemical pollutants is prepared by diluting an appropriate amount of mixed standard solution with
blank extract, which has been taken through the method with the rest of the samples. Mix thoroughly.
Used for plotting the standard curve.
Working standard mixture solution in matrix must be prepared freshly.
Candidates for 2016 Method of the Year
274